[Boatanchors] Carbon Comp Resistors

[Richard Knoppow]

    Carbon composition resistors are sensitive to heat and 
moisture. I think the ones that drift the least are those with 
the best moisture seal. I suspect baking them will make them 
drift more.
     The best of the old resistors seem to be the Allen-Bradley 
ones also sold by Ohmite. The identity of the two brands is 
established in Ohmite advertising which states it. I see very few 
IRC composition resistors in equipment so don't know how they 
compare. IRC had a different filler, something they called 
"metalized". The don't seem to have been more expensive so I 
don't know why they are relatively uncommon.
     As far as current prices, keep in mind the rate of 
inflation, since the 1950s prices have increased by something 
like ten times so a resistor costing a dollar now would have sold 
for ten cents then. What has happened is the price of film 
resistors has dropped substantially. While once more expensive 
than composition they have become cheaper by about the amount 
inflation. I think the main difference is that most of the hand 
work has been eliminated while production methods for composition 
has probably not changed much. Plus the market for composition 
has shrunk.

On 5/6/2020 8:58 AM, jeff bauman via Boatanchors wrote:
> I too have endless miles of old carbon comp resistors.  And just about all of them have changed value.IIRC, i have read where some have had success bringing them back to value by heating them in an oven, but I think most have discarded that treatment as ineffective.So ... my question is:  can I use a resistor that say, has drifted up 40% to 100K ohms as a 100K ohm resistor?  Is it apt to stay within 10% tolearnce after use?Guessing this has been "asked and answered" but hopefully someone can indulge me on this list.Thanks.JeffW8KZW
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL